1. FIELD OF THE INVENTION
The present invention concerns a torsional damper comprising at least two coaxial parts mounted to rotate relative to one another within a defined range of relative angular movement and circumferentially acting elastic means between said parts resisting such relative angular movement over at least part of said range of relative angular movement.
2. DESCRIPTION OF THE PRIOR ART
This type of torsional damper is normally incorporated in the design of a friction clutch, particularly for automotive vehicles, in which case one rotating part comprises a friction disk designed to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automotive vehicle, whereas another of said rotating parts is carried on a hub designed to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automotive vehicle.
This type of torsional damper is used to permit regulated transmission of rotational torque applied to one of its rotating parts where the other is itself subject to a rotational torque. It is thereby able to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automotive vehicle.
The present invention is more particularly directed to the case where at least one of the two coaxial parts comprises a transverse annular flange, in the form of a hub flange or guide ring.
In practice, each of the two coaxial parts normally comprises an annular flange of this kind. For example, a first of the coaxial parts may comprise a hub flange, usually coupled to a hub, whereas the other comprises two spaced parallel guide rings attached together by spaced axial spacers, one on each side of the hub flange; in the case of a friction clutch for automotive vehicles, it is then to one of these guide rings that the friction disk is usually attached, this guide ring having for this purpose circumferentially spaced holes each adapted to have a fixing means, such as a rivet, for example, pass through it, and by means of which a friction disk of this kind is thus attached to it.
However, a reverse arrangement is also possible in which the two guide rings are coupled to the hub whereas the hub flange, unrestricted relative to said hub, carries the friction disk.
More often than not, the circumferentially acting elastic means employed consist of elastic members such as helical coil springs or elastomer blocks, for example, extending tangentially relative to a circumference of the assembly and the two coaxial parts concerned have registering openings adapted to accommodate these elastic members.
In practice, these openings consist of windows formed for this purpose in the annular flanges of said coaxial parts and there are provided a number of separate groups of elastic members having different stiffnesses, the coming into action of which during relative angular movement between said coaxial parts being modulated by appropriate differences between the circumferential dimensions of the corresponding windows, the elastic members of less stiffness being the first to come into action before the effect of the elastic members of higher stiffnesses is successively added to them.
It has already been proposed, as described in U.S. patent application Ser. No. 317,175 dated Nov. 2, 1981, now U.S. Pat. No. 4,496,036, to replace the elastic members of lower stiffness with elastically deformable arms superposed in the axial direction on the coaxial parts concerned and adapted to act in the circumferential direction between the latter.
As soon as relative angular movement between these coaxial parts begins, these elastically deformable arms come into action, acting alone at this time; at later stages of this relative angular movement other elastic members, of greater stiffness, add their effect to those of the arms and it is essentially these latter elastic members which give the torsional damper its torque transmission capacity in the final stage of such relative angular movement.
It has also been proposed, as described in U.S. patent application Ser. No. 343,578 dated Jan. 28, 1982, now U.S. Pat. No. 4,480,736, to use elastically deformable arms adapted to come into action during the final phases of the relative angular movement between the coaxial parts concerned, each of these elastically deformable arms being supported at one end by one of said coaxial parts while the other end is unsupported and features a shoulder through which it is adapted to engage with a shoulder provided for this purpose on the second of said coaxial parts.
Unlike the previous arrangement, it is then necessary, with an arrangement of this kind, for a certain degree of relative angular movement to have already occurred between the coaxial parts concerned before, these shoulders then coming into engagement with one another, the elastically deformable arms employed come into action, and the torque transmission capacity of the assembly in the final stage of said relative angular movement is then essentially due to these arms.
These arrangements are satisfactory.
However, in practice, the second at least is highly specific to the particular torsional damper concerned.
The latter must therefore be designed according to the intended application.
A general problem which arises in designing torsional dampers of the kind under discussion is to optimize the standardization of the component parts, whatever the specific application conditions, so as to minimize costs.
Incidentally, this is the reason why, in the case of a friction clutch for automotive vehicles, when one of said coaxial component parts of a torsional damper of this kind comprises, independently of the hub, two annular flanges forming guide rings, these guide rings are identical and both have circumferentially spaced holes for attaching a friction disk, although only one of them is in reality intended to carry a friction disk of this kind.
As a corollary to this, and for the same reasons, it is beneficial to use identical guide rings for different applications, in spite of them then having the same arrangement of windows for accommodating elastic members.
In the case of an automotive vehicle marketed in two versions, a standard version and a turbocharged version, for example, the torsional damper used in the turbo version must have increased torque transmission capacity in the final stage of relative angular movement between the two coaxial parts which constitute it.
Likewise, it may be beneficial to be able to fit an automotive vehicle with a friction clutch providing different torque transmission capacities when the torque is increasing and when the torque is decreasing.
A general objective of the present invention is to provide an arrangement which can meet such objectives whilst also satisfying the requirements for standardization.